Author
Topic: Freelance Inline Twin (Read 34453 times)

The days are getting shorter and the temperatures cooler, which draws one back into the shop. So itís time to introduce you to my next project. After the hit Ďn miss engine I built last, I want to build a multi cylinder engine. Iíll keep it relatively simple, as it will be a two cylinder engine.

The engine is totally freelance and designed by myself. The main part of my design is the built up crankshaft. The inspiration for the crankshaft comes from H. Shillings. It utilizes large thin section ball bearings to register the different parts accurately. The idea is to have easy to make parts that will be assembled to a true running crankshaft.

The goal will be to have a slow idling, well running engine. I set the compression ratio at 5.5 : 1. This figure is just a stab in the dark, as I havenít built an engine like that before. The slow idle is important to me, and I feel I can achieve what Iím looking for with the mass of the flywheel and crankshaft combined.

The engine is built up from bar stock. Throughout the design, I tried to simplify the parts as much as possible without compromising the look too much.

It will be liquid cooled, requiring a full set up with pump, fan and radiator and all. Thatís another first for me.

A few dimensions to get a feel for the size; Bore 32mm, Stroke 34mm, Flywheel diameter 90mm, Height to top of cylinder head 178mm

Below, I have some CAD renderings for you guys. This is how the finished engine should look like. There are still a few little details that need attention, but I feel confident enough in the design to have a go at it.

Looks an interesting project Is that the waterpump behind the fan? I'm not sure that you will really need the number of crankshaft bearings that you have unless you will be running the engine with high loads/speeds

Looks Intertesting, Malcom Stride had a couple of basic designs using the Schillings type crank but never got round to making them, not unlike your engine in many ways.

Roger the bearings form part of the crankwebs and without them the built up crankshaft would not work, Schillings used the method in a number of engines upto V8 or maybe even a V10. Though I think it should only need the centre bearing and two small outer ones.

Roger, yes, that is the pump behind the fan.Like Jason said, the bearing are an important part of the built up crankshaft, and not only for the load bearing. Especially for our small engines. The outer bearings could be smaller, but when I started to draw up this project, it was a four cylinder, which I then reduced to two. I left it modular like that to test the design.It is an experiment, even though I have confidence it will work well. I guess the only way to find out is to build one...

Very nice project, i enjoy to follow this thread...I didn't see any output from the camshaft to drive the distributor, are you planning to use glow plugs ?

I have an inline four (still unfinished) with this sort of crankshaft and when all the pieces are apart on the bench, it looks very tricky to assemble in the engine bloc...but really clever at the end!!

Yogi,On thing you might think of in the initial design stages is to make accommodation for a one-way bearing in the flywheel for starting purposes. Since I adopted this type of setup on my engines for starting it sure makes it much simpler. Another thing I noticed it doesn't look like you have much room between the camshaft and the pushrod to allow for lifters. gbritnell

Zephyrin, I'm planing on an electronic ignition, with a lost spark. Both plugs firing at the same time, so no need for a distributor. I like the crankshaft you built there. That is exactly along the lines of what I'm trying to do here.

George, thanks for your input. Not sure what you mean with a one way bearing, like a overrunning clutch? If so, yes, I have thought about it. The crankshaft will have a thread at the end of it (it's not modeled in the rendering, just showing the major diameter). The reason for that is I'm not sure what the engine is going to drive if anything. I'm hoping it would be a candidate to drive a generator. A little genset. The thread leaves me with options on how to adapt it to different things, including a starting dog.Please see the cross section of the cam/lifter arrangement. The guides are threaded into the block, and could easily be made longer if need be. Any feedback is greatly appreciated.

Thanks Brian, you know I like to work in metric, as there are fewer decimal points!!!

This promises to be very interesting, Yogi. I like the layout so far. I do question having both crank throws in line as I've never seen an engine like that. Usually the two throws are 180* apart. Will it balance the way you have it drawn??

Pete, I debated hard over a 360 vs a 180 degree crank. I ended up deciding on a 360 degree crank even though the imbalance is a concern. The big advantage of this design is if it doesn't work, it will be a matter of undoing two screws and I can change it to a 180 degree crankshaft.